1. Field of the Invention
The invention relates to a method for starting a sensorless, electronically commutatable direct current motor.
2. Description of the Prior Art
One method of starting electronically commutated direct current motors is known for instance from the dissertation D 93 by Volker Bosch at the University of Stuttgart, entitled “Elektronisch kommutiertes Einzelspindelantriebssystem” [Electronically Commutated Single-Spindle Drive System], Shaker Verlag, Aachen, 2001. In such electronically commuted direct current motors, which do not detect the rotor position via sensors, the absolute position of the rotor at a standstill is not known. For initial positioning of the motor, the rotor is therefore first put in a predetermined outset position at the onset of the startup operation, which is done by supplying two or three phases of the motor with current, so that the rotor aligns itself accordingly. After a defined waiting period, a controlled startup of the motor then takes place by incremental delivery of current to further phases of the motor. The method for sensorless rotor position detection described in the aforementioned publication, however, on principle furnishes a reliable position signal only above a predetermined minimum rpm of the rotor, and this method can therefore not be used directly for starting the motor. The motor startup is thus done in a controlled way rather than regulated; that is, blocking of the rotor cannot be immediately detected and corrected. For motors with variable loading, this known method is therefore only conditionally suitable.